Tension device



June'zz, 1943."

J. GOULDBOURN TENSION DEVICE 'F'iled Sept. 20,;1959

2 SheetS -Sheet 1 Jun 22, 1943. J, soQLpBoURN TENSION' DEVICE Filed Sept20, 1959 2 Sheets-Sheet 2 Patented June 22; 1943 TENSION DEVICE JosephGoul'dbourn, Leicester, England, assignor to United Shoe MachineryCorporation, Borough of Flemington, N. 1., a corporation of New JerseyApplication September 20, 1939, Serial No. 295,780 In Great BritainNovember 3, 1938 '17 Claims.

This invention is concerned with improvements in or relating to tensiondevices or to machines making use of the same. I

The invention will hereinafter be explained by way of illustration, andnot of limitation, in connection with sewing machines and, inparticular, in connection with a curved hooked needle chainstitch sewingmachine organized for use in the manufacture of boots or shoes. Anexample of such a machine as last mentioned is that illustrated in thepatent to Eppler No. 1,076,201, dated October 21, 1913.

Curved hooked needle chainstitch sewing machines for sewing the inseamsof boots or shoes commonly include a thread tension device comprising apair of thin discs providing between them a peripheral V-shaped groovewhich receives the thread passing around the discs and, in order toprevent too free rotation of the discs as the thread is drawn roundthem, a braking action is exerted on the discs by means of a relativelystationary brake-shoe thrust by a spring against the periphery of abrake drum secured to the discs. Suitable means is provided in suchmachines for automatically varying the pressure of the brake-shoeagainst the drum at different times in each stitch-forming cycle so thatthe thread may run more freely through the machine at some stages in theformation of the stitches than at others.

The brake-shoe, being relatively stationary, applies a dead pressureagainst the periphery of the brake drum and at certain times in theoperation of the machine (for example either at the commencement of theformation of each stitch or during the thread pulling-off action of theusual take-up or during the thread pulling action of the needle as itretreats after having penetrated the between-substance), the operationof the various thread-handling instrumentalities causes thread to bedrawn relatively rapidly around the tension discs and thus causes thetension discs either to start into actual rotation or to move with anaccelerated motion if they are already rotating. However I have foundthat the force necessary either to set the discs into rtation from restor to cause them to rotate with an accelerated motion while they areactually rotating is considerably greater, in such a tension device asabove referred to, than the force necessary to keep the discs rotatingat a uniform speed. This fact not only causes the tension applied by thedevice on the thread at different times in the machine cycle to varyconsiderably from that which would produce the best results in theformation of the successive stitches but also, by making it necessarywhen initially adjusting the tension device prior to the commencement ofa sewing operation to allow for such unwanted but unavoidable increasesin the tension on e thread, often makes it impossible so to set themachine as to cause the stitches to be drawn as tightly against the workas desired.

The above-mentioned tendency of the tension device to exert aconsiderably increased tension on the thread when it is attempted todraw thread more rapidly around the discs or when the stationary threadis initially pulled around them on the commencement of the formation ofeach stitch arises, so it is believed, not so much from the actualinertia due to the weight of the discs themselves as from thedead-weight nature of the braking action exerted on the discs which hasto be overcome.

It is one of the several objects of the present invention to provide animproved form of tension device of such a nature that it will be able toexert a more nearly uniform degree of tension on thread passing aroundit in spite of variations in the speed at which the thread is pulledaround itthus not only contributing to a more uniform setting of thesuccessive stitches against the work but also making it possible, byinitial adjustment of the, device, to make sure that the stitches willbe uniformly pulled as hard against the work as is justified by thequality of the work and/or the strength of the thread.

To this end a particular illustrative 'embodi ment hereinafterdescribed, of the present invention embodies a pair of thread tensiondiscsof somewhat conventional form which, instead of having adead-weight braking action exerted on them by a relatively stationarybrake shoe as hitherto, hav a braking action exerted on them by afriction disc which bears against a member secured to the tension discsand, is rotated at a constant low speed (e. g. about 60 R. P. M.assuming. the machine to be making some 600 stitches per minute) and ina direction opposite to that in which the discs are rotated by thepassage of'the thread therearound. The said friction disc commences torotate in this direction, and thus exerts, a live backward drag on thetension discs, immediately the machine is started into operation afterthe presentation of work to it and continues uniformly so to rotateuntil the machine is actually brought to rest. In spite however of theconstant backward rotation of the friction disc and of the fact that itbears against a member secured to the tension discs, the latter discsare not allowed to rotate backwafdly with it but, on the contrary, areheld from so doing by a pawl and ratchet device and this fact bringsabout the result that a slippage,

' bringing about a predetermined degree of live frictional torque, takesplace between the friction disc and the tension discs.

The application to the tension discs of such a constantly backwardlyexerted frictional effort has, during tests of such a tension device asabove Ltd indicated, shown itself to be of considerable benefit both inallowing the tension discs to apply a substantially even tension to thethread throughout the various desired stages of each stitch formingcycle and in allowing the discs to rotate forwardly from rest, when thethread is initially pulled around the discs at the commencement of eachstitch forming operation of the machine, without exerting on the thread(by reason of undue resistance to such forward rotation) a degree oftension substantially higher than that needed to maintain the discs inforward movement once they have started from rest.

However it is desirable that the tension device should exert a reducedtension on the thread at that time in the machine cycle when the needeis retiring through the work, after having penetrated it, and is drawinga loop of thread therethrough. For this purpose the device of saidillustrative embodiment includes a pair of compression springs whichserve to thrust the said rearwardly moving friction disc into bearingcontact with the member which is secured to the tension discs andautomatically acting means is provided for causing both said springs tocooperate in thrusting the friction disc and the member together duringthe greater part of each sewing cycle but to cause one of them to becomeinoperative (thus reducing the pressure between the friction disc andthe member) during the retiring movement of the needle. Moreover saidmeans acts automatically to render both said springs inoperative tothrust the friction disc and member together when the machine comes torest at the end of a sewing operation thus allowing the tension disc tobe rotated freely while the machine is idle, preparatory to thecommencement of another sewing operation, and thus allowing the operatorto draw thread easily through the machine ready for the recommen-cementof the machine into operation on another boot or shoe.

It will be understood that the present invention in its broader aspectsis not limited in its application to an inseam chainstitch shoe sewingmachine of the type described, but may well be applied to other types ofmachines for operating upon heavy work such as leather, having threadhandling devices including means for intermittently drawing off threadfrom the supply wherein it will be of advantage to provide applicantsimproved thread tension embodying therein a thread engaging member suchas a tension wheel, and a friction device acting thereon having means tomaintain a continuously live frictional resistance to the movement ofthe thread engaging member which will eliminate uncertainties orvariations in the thread tension due to added frictional resistanceordinarily encountered in starting or in accelerating the drawoffmovement of the thread engaging member.

With the above noted and other objects in view, as may hereinafterappear, the several features of the invention consist also in thedevices, combinations and arrangement of parts hereinafter shown anddescribed, which together with the advantages to be obtained thereby,will be readily understood by one skilled in the art from the followingdescription taken in connection with the accompanying drawings, in whichFig. 1 is a view in left side elevation of the sewing head of achain-stitch inseam shoe sewing machine illustrating a preferredembodiment of the invention, only so much of the machine having beenillustrated as is necessary to show the connection of the inventiontherewith; Fig. 2 is an enlarged detail view of applicants improvedthread tension shown in Fig. 1; and Fig. 3 is a sectional view taken onthe line 3--3 of Fig. 2.

The shoe machine illustrated in the drawings as embodying in a preferredform the several features of the present invention, is adapted forsewing the upper and insole of a welt shoe, and

1 tension, and is again drawn in against a thread tension during thethread drawing stroke of the take-up, which acts to tighten the previousloop against the shank of the needle after the needle has entered thework, and to draw oif additional thread from the supply against thetension. In the preferred embodiment illustrated in the drawings, atensioning device is employed which is capable of applying a relativelylight tensioning strain on the thread during the needle loop drawingstroke, and of applying on the thread a considerably heavier tensioningstrain during the loop drawing stroke of the take-up. in order totighten the previous stitch. In each instance, it is desirable to adjustthe tensioning strain on the thread as accurately as possible inaccordance with such factors as the quality and nature of the work andthe strength of the thread employed.

With the thread tensioning devices of the prior art in which thecooperating friction surfaces are normally stationary and are movedrelatively to one another only upon starting the tension wheel, it hasbeen necessary in adjusting these tensions, to take into account theadditional ten sioning strain on the thread and on the work required tostart the tension wheel both at the limit of the loop drawing stroke ofthe needle, and again as the take-up approaches the limit of its loopdrawing stroke, to draw off additional thread from the supply. Correctadjustments of such thread tensioning devices of the prior art are madestill more difiicult by the fact that the amount of force required tostart the friction surfaces from a relatively stationary position is notdirectly dependent upon the frictional engaging pressure, but may varyconsiderably as the surfaces become more or less firmly set in astationary position.

Referring specifically to the drawings, the illustrative embodimentcomprises a bracket 2 8 which is secured on the rear of the head 22 ofthe sewing machine and which has a bearing for a horizontal tensionshaft 25 extending laterally of the machine. Secured on the left end ofthe said shaft 26 is a thread wheel 26 around which the thread passesfrom its source of supply to the stitch forming devices of the machine.The thread wheel 2:: is formed of two discs secured together. The outermargin of each disc is notched and the projecting portions of the discsbetween adjacent notches are bent away from each other so as to form aV-shaped groove in hich the thread lies. The tension shaft 24 has formedon its right hand end a ratchet wheel 28, the teeth ofwhich are engagedby two pawls 30 and 32 which are pivoted on the bracket and are urgedtowards the ratchet wheel by spring plunger 34 and 36. The pawls 30 and32 are so arranged that when one is in engagement with a tooth on theratchet wheel 28 the other engages the ratchet wheel about half-waybetween two adjacent ratchet teeth on the wheel. Said pawls cooperatewith the teeth on the ratchet wheel to prevent rotation of the threadwheel 26 in a direction opposite to that in which it is moved by thepassage of the thread therearound.

The tension shaft 24 is rotatably mounted in a sleeve 38 which isrotatably mounted in the said bearing and the sleeve 38 has formed onits righthand end a flange 49 in which is secured a friction ring 42which engage the left-hand face of the ratchet disc28. Between theflange 40 and the end of the bearing is an anti-friction ball bearing4.4. The flange 46 has formed on its outer peripheral face gear teeth 46which mesh with a worm gear 43 on a worm gear shaft 50 which isrotatably mounted in bearings in the bracket 20 below the tension shaft24. The worm gear shaft 50 has secured on its forward end a groovedpulley 52 around which passes a belt and the belt also passes around asecond pulley which is driven whenever the machine is being operated.The flange 40 is driven in the opposite direction to that in which theaforesaid thread wheel 25 is rotated when the thread is being drawn fromthe supply during the operation of the machine. The engagement of one ofthe aforesaid pawls 39 or 32 with a tooth on the ratchet Wheel 28prevents the thread wheel 25 from being rotated with the flange 40 inspite of its frictional engagement with the friction ring 42. The factthat the thread wheel 26 is prevented from rotating backwardly with thefriction ring 42 brings about the result that a constant, slippageoccurs between the thread wheel 26 and the friction ring 42 and thisslippage has the effect of exerting a constant torque on the threadwheel 26 which can be overcome by a smooth and predetermined, but notexcessive, amount of tension exerted on the thread when the latter tendsto rotate the thread wheel 26 forwardly.

The'ratchet wheel 28 is pressed against the aforesaid friction ring 42,which may be of cork or a composition of cork and other material, by twocompression springs 54, 58 arranged one within the other which are inaxial alignment with the axis of the tension shaft 24, the pressure ofthe springs against the ratchet wheel being controlled through means newabout to be described.

The left-hand end of the inner spring 54 engages a collar 58 which isupported in the lower forked end of one arm 6 of a bell-crank lever 52which is pivoted on a horizontal forwardly and'rearwardly extendingshaft 64 secured to the bracket 20. The arms of the fork have extendingthrough them horizontal screws, the inner ends of which enter recessesin the opposite sides of the collar 58.

Between the left-hand end of the collar '58and the aforesaid ratchetwheel 28 is a ball thrustbearing 66. The right-hand end of the innerspring 3 ls engaged by a flanged plug 68 which is engaged by ahorizontal adjusting screw is rotatably mounted in an arm 12 extendingto the right from the bracket 20 and secured thereto. The screw if! hasa comparatively large head which has indicating marks around itsperiphcry and the arm 12 has secured to it a scale 14 parallel to thescrew and close to it, which also has indicating marks on it. Theindicating marks assist the operator in adjusting the spring 54 by meansof the screw and enable the operator to readily return the spring to aprevious adjustment thereof if desired. The screw 10 is held securely inits adjusted position by means of a locking screw 15 mounted on the arm12 at right angles to the screw Ill for locking engagement therewith.

The outer spring 55 engages a second collar 16 which normally engagesthe first collar 58. The second collar 16 is supported on the ends ofhorizontal pins l8, 18 extending inwardly from the arms of a fork at thelower end of an arm 82 of a second bell-crank lever 84 pivoted on thesame shaft 64 as the first mentioned bellcrank lever 62. The other endof the second spring 56 is received in a recess in an adjustable collar85 which surrounds the screw 19 and spring 54 and which is adjustablymounted in the aforesaid arm 12 on the bracket Zll. The adjustablecollar 85 has formed thereon a flange 81 by which it may be rotated toadjust the spring 56 and the peripheral face of the flange has on itindicating marks. The peripheral face of the flange of the collar 86 isclose to the aforesaid scale 14 and the marks on the face and marks onthe scale assist the operator in adjusting the collar or returning it toprevious adjustment.

The aforesaid thread wheel 26, Worm gear 48 and flange 40 are housedwithin the bracket 20, the thread wheel being in a recess 88 which isclosed by a cover plate 90 pivoted on the bracket. The flange and wormgear are housed within a second recess in the bracket and the frictionring lies just within this recess.

The aforesaid bell-crank levers 62, 84 have more or less horizontal arms92, 54 extending towards the left from their pivot 64. The horizontalarm 94 of the second bell-crank lever 84 is arranged to be engaged by ascrew 95 in a rearwardly extending arm 98 of a cam actuated l bell-cranklever which is pivoted on a horizontal shaft I00 extending laterally ofthe machine. An upwardly extending arm I02 of the latter bell-cranklever carries a cam roll I04 at its upper end which is held against acam on the cam shaft of the machine by a spring I06.

During the operation of the machine both springs 54, 56 act to cause theratchet wheel 28 to be pressed against the friction ring 42 on theaforesaid flange 40 (which is being comparatively slowly rotated, i. e.,at about 60 revolutions per minute, in the opposite direction to that inwhich the thread wheel 26 is rotated by a pull on the thread passingaround it) during the whole of the machine cycle except during thatportion when the needle is moving rearwardly and drawing a' loop ofthread through the work and is also drawing thread from the supply. Justbefore the needle commences to move rearwardly and while the looper islaying the thread in the needle barb the bell-crank lever 84 is actuatedby its cam to relieve the pressure of the second spring 56 on theratchet wheel 28 and 'just before the needle commences to move forwardlyagain the pressure of the second spring 56 against the ratchet wheel 28is again applied and is continued until just before the needle commencesto move rearwardly again.

U The thread therefore is under a lighter tension (due to thepartialQrelief in the pressure with which the ratchet wheel and frictionring are pressed together) when the needle is moving back than at othertimes in the machine cycle.

The horizontal arm 92 of the first bell-crank lever 62 is arranged to bedepressed by stopping mechanism of the machine as the machine comes torest, to release the thread tension. As best shown in Figs. 1 and 3, thearm 92 is arranged to be acted upon by an adjustable stop screw 5 IE onone arm of abell-crank lever I I2 mounted to turn on a pivot stud H4.The other arm of the bell-crank H2 is connected by links H5, H! to alever H8 supported to turn on the shaft IEO. A shifter lever inconnected to an upwardly extending arm of the lever H8 is renderedoperative by the rotation of the main cam shaft 224 in a reversedirection in stopping the machine to rock the lever H8, causing thebellcrank H2 to be rocked in a direction to depress the arm 52. Whenthis arm of the bell-crank lever 62 is depressed, its other arm 63 whichcarries the first collar 58 is swung towards the right and moves bothcollars 58, 76 away from the ratchet wheel 28 against the pressure ofboth springs 54, 5'3, and thus releases the pressure of the ratchetwheel 28 against the rotating friction ring 42 so that the thread wheel26 can rotate freely and allow thread to be drawn freely by the operatorfrom the supply.

It will be apparent that the illustrative embodiment comprises a tensiondevice for a chainstitch shoe sewing machine in which the drawing ofthread from the supply is resisted by the relative movement of frictionfaces pressed together by springs and in which one of the friction facesis continuously rotated, while the machine is in operation, in theopposite direction to that in which the other face is rotated by thedrawing of the thread from the supply by the stitch forming devices ofthe machine, the device also including means for preventing the latterface from being rotated backwardly by the first mentioned face at alltimes when the thread is not tending to rotate it forwardly. Suchrelative movement of the friction faces provides a live tension whichenables the thread to be readily drawn from the supply at thecommencement of such drawing of thread and provides at all times whenthe machine is being operated a substantially uniform tension enablingthe thread to be drawn smoothly from the supply.

The invention having been described, what is claimed is:

1. In a machine having thread handling devices including means forintermittently drawing off thread from a supply, a thread tensionincluding a thread engaging member movable intermittently with thethread, and a friction device acting upon said thread engaging member,said friction device comprising cooperating friction surfaces, and meansfor relatively moving said friction surfaces to provide a livefrictional resistance effective to reduce the resistance to the startingof said member.

2. In a machine having thread handling devices including means forintermittentl drawing off thread from a supply, a threadtension'including a thread engaging member movable intermittently withthe thread, and a friction device acting upon said thread engagingmember comprising cooperating friction surfaces, and means forrelatively moving said friction surfaces continuously to maintain a livefrictional engagement therebetween.

'3. In a machine having thread handling devices including means forintermittently drawing oif thread from a supply, a thread tensionincluding a thread engaging member movable intermittently with thethread, and a friction device acting upon said thread engaging membercomprising cooperating friction surfaces arranged for continuousrelative movement to maintain a live frictional engagement therebetween.

4. In a machine having thread handling devices including means forintermittently drawing off thread from a supply, a thread tensionincluding a thread engaging member movable intermittently with thethread, and a friction device acting upon said thread engaging membercomprising cooperating friction surfaces, tensioning means for exertinga frictional engaging pressure between said surfaces, and means forrelatively moving said friction surfaces continuously to maintain a livefrictional engagement therebetween.

5. In a machine having thread handling devices including means forintermittently drawing oif thread from a supply, a thread tensionincluding a thread engaging membermovable intermittently with thethread, and a friction device acting upon said thread engaging membercomprising cooperating friction surfaces, tensioning means for exertinga frictional engaging pressure between said surfaces, adjusting meansfor adjusting the pressure exerted by said tensioning means to any oneof a plurality of predetermined values, and means for relatively movingsaid friction surfaces continuously to maintain a live frictionalengagement therebetween.

6. In a machine having thread handling devices including means forintermittently drawing off thread from a supply, a thread tensionincluding a thread engaging member movable intermittently with thethread, and a friction device comprising a friction member frictionallyacting on said thread engaging member, and means for continuously movingsaid friction member relatively to the thread engaging member tomaintain a live frictional engagement of the friction member with thethread engaging member.

7. In a machine having thread handling devices including means forintermittently drawing off thread from a supply, a thread tensionincluding a thread engaging member movable intermittently with thethread, and a friction device comprising a friction member frictionallyacting upon said thread engaging member, means for continuously movingthe friction member in a direction opposite to the draw-off movement ofthe thread engaging member with the thread, and means to preventmovement of the thread engaging member with the friction member.

8. In a machine having thread handling devices including means forintermittently drawing off thread from a supply, a thread tensionincluding a tension wheel over which the thread passes from the supply,a friction surface associated with the tension wheel, a friction memberfrictionally engaging with and rotatable with relation to said frictionsurface, tensioning means for maintaining a frictional engaging pressurebetween said surface and friction member, means to prevent rotation ofthe tension wheel in a reverse direction, and means for continuouslyrotating the friction member in said reverse direction to maintain alive frictional engagement beif;ween the friction member and thefriction surace.

9. A chainstitch shoe sewin machine having,

in combination, thread handling devices including a needle, a looper, atake-up, and a thread. tension comprising a tension wheel from whichthread is intermittently drawn off from the supply by the threadhandling devices, and a friction device acting upon said tension wheel,said friction device comprising cooperating friction surfaces, and meansfor relatively moving said friction surfaces to provide a livefrictional resistance effective to reduce the resistance to the startingof the tension wheel.

10. A chainstitch shoe sewing machine having, in combination, threadhandling devices including a needle, a looper, a take-up, and a threadtension comprising a tension wheel over which thread is intermittentlydrawn off from the supply by the thread handling devices, a frictiondevice acting upon said tension wheel comprising cooperating frictionsurfaces, and means for relatively moving said friction surfacescontinuously to maintain a live frictional engagement therebetween toresist the starting of the tension wheel.

11. A chainstitch shoe sewing machine having, in combination, threadhandling devices including a needle, a looper, a take-up acting to pullthe thread tightly around the needle while the needle is in the work,and to draw off additional thread from the supply, and a thread tensionagainst which the take-up acts comprising a thread engaging membermovable with the thread, a friction member frictionally acting upon saidthread engaging member to tension the thread, and means for continuouslymoving said friction member to maintain a continuously live frictionalresistance to the starting of said thread engaging member.

12. A chainstitch shoe sewing machine having, in combination, threadhandling devices including a needle movable to draw in a loop of needlethread, a looper, a thread finger, and a take-up movable to give upthread and thereafter to pull the thread tightly around the needle whilethe needle is in the work, a thread tension including a tension wheel, afriction surface associated therewith, a friction member engaging saidsurface and rotatable relatively thereto, tensioning means formaintaining frictional engagement between said surface and frictionmember, means to prevent rotation of the tension wheel in a reversedirection, and means for continuously rotating said friction member insaid reverse direction to maintain a live frictional resistance to thestarting of the tension wheel.

13. A chainstitch shoe sewing machine having, in combination, threadhandling devices including a needle movable to draw in a loop of needlethread, a looper, a thread finger, and a take-up movable to give upthread and thereafter to pull the thread tightly around the needle Whilethe needle is in the work, a thread tension including a tension wheel, afriction surface associated therewith, a friction member engaging saidsurface and rotatable relatively thereto, tensioning means formaintaining frictional engagement between said surface and frictionmember, means to prevent rotation of the tension wheel in a reversedirection, means for continuously rotating said friction member in saidreverse direction to maintain a live frictional resistance to thestarting of the tension wheel, and means operative in stopping themachine to relieve the tension between the surface and friction member.

14. A chainstitch shoe sewing machine having, in combination, threadhandling devices including a needle movable to draw in a loop of needlethread, a looper, a thread finger, and a take-up movable to pull thethread tightly around the needle while the needle is in the work and todraw off additional thread from the supply, a thread tension including atension Wheel, a friction surface associated therewith, a frictionmember engaging said surface and rotatable relatively thereto,tensioning means constructed and arranged to apply a frictioning tensionof a predetermined value between said surface and friction member duringthe loop drawing stroke of the needle and a frictioning tension of apredetermined greater value between said surface and friction memberduring the tightening of the thread by the take-up, means to preventreverse movement of the tension wheel, and means for continuouslyrotating said friction member in said reverse direction to maintain alive frictional resistance to the starting of the tension wheel.

15. A chainstitch shoe sewing machine having, in combination, threadhandling devices including a needle movable to draw in a loop of needlethread, a looper, a thread finger, and a take-up movable to pull thethread tightly around the needle while the needle is in the work and todraw off additional thread from the supply, a thread tension including atension wheel, a friction surface associated therewith, a frictionmember engaging said surface, means for continuously rotating thefriction member in a direction reverse to the draw-off movement of thetension wheel, means to prevent movement of the tension wheel in saidreverse direction, a normally operative tension mechanism for exerting aconstant frictionally engaging pressure between said sur face andfriction member during operation of the machine, a supplementary tensionmechanism operative durin the loop tightening movement of the take-up,and means operative in stopping the machine to relieve both tensionmechanisms.

16. A thread tension of the character described which comprises atension wheel over which the thread is drawn off, a friction surfaceassociated with the tension Wheel, a friction member engaging saidsurface, means for continuously rotating the friction member in adirection reverse to the draw-off movement of the tension wheel, meansto prevent rotation of the tension wheel in said reverse direction, andtensioning means for exerting a predetermined frictional engaginggressure between said surface and friction mem- 17. A thread tension ofthe character described which comprises a tension wheel over whichthread isdrawn off, a friction surface associated with the tensionwheel, a friction member engaging said surface, a worm and worm wheeldriving connectionfor continuously rotating the friction member in adirection reverse to the draw-off movement of the tension Wheel, a pawland ratchet connection to prevent rotation of the tension wheel in saidreverse direction, and tensioning means comprising a spring andadjusting means therefor for exerting a predetermined frictionalengaging pressure between said surface and friction member.

JOSEPH GOULDBOURN.

